Screen with differently tensioned surface zones

ABSTRACT

A sifting machine has a strainer box defining feed-in and discharge points and a free sieve netting surface arranged and tensioned in the strainer box so that a material flow-path is defined across it from the feed-in point to the discharge point. A plurality of striker assemblies may also be arranged in the strainer box for exciting the netting surface. A plurality of fastening and tensioning devices such as clamps are provided along the edges of the netting which are parallel to the direction of the material flow-path for individually tensioning the netting, in a direction transverse to the flow-path, at different points spaced in the direction of the flow-path such that the netting is transversely tensioned to different tensions along the direction of the flow-path. Similar devices may be provided along at least one edge of the netting parallel to the material flow-path for individually tensioning the netting, in the direction of the flow-path, at different points spaced transversely to the direction of the flow-path. The striker assemblies may be operated synchronously or asynchronously.

United States Patent Krause [45] Dec. 19, 1972 154] SCREEN WITHDIFFERENTLY 2,114,406 4/1938 Simpson ..209/408 x TENSIONED SURFACE ZONES2,134,240 10/1938 Sowder .L ..'....209/382 [72] Inventor: Rudolf J.Krause, Bad Homburg, FOREIGN PATENTS OR APPLICATIONS Germany 627,0275/1927 France ..209/403 73] Assignee; Rhewum Rheinische w 578,893 7/1924France ..209/403 Machinenfabrik G.m.b.l'l., I Remscheid-Luttringhausen,Ger- Primary Examiner-Tm many Assistant lixaminer Ralph J. H1llAttorney- Spencer & Kaye [22] Filed: June 15, 1970 1211 Appl. No.546,197 [57] ABSTRACT v A sifting machine has a strainer box definingfeed-in and discharge points and a free sieve netting surface [30]Forelgn Application Pnomy Dam arranged and tensioned in the strainer boxso that a June 13, 1969 Germany ..G 69 23765.6 material flow-path isdefined across it from the feed-in point to the discharge point. Aplurality of striker as- [52] US. Cl. ..209/347, 209/365, 209/382,semblies may also be arranged in the strainer box for 209/404 excitingthe netting surface. A plurality of fastening [51] lnt. Cl. ..B07h 1/34and tensioning devices such as clamps are provided [58] Field of Search.Q209/357, 322, 323, 319, 347, along the edges ofthe netting which areparallel to the -209/382, 404, 408, 364, 365 R, 313, 368, direction ofthe material flow-path for individually 310,- 319, 403 tensioning thenetting, in a direction transverse to the flow-path, at different pointsspaced in the direction of 5 Refe'rences Cited the flow-path such thatthe netting is transversely tension'ed to different tensions along thedirection of the UNITED STATES PATENTS flow-path. Similar devices may beprovided along at 2,804,208 8/1957 Van Hardefeld etal. ..209/403 leastedge of the netting Parallel to the material 1,904,032 4/1933Roberts....- ..209/382 x individually tensioning netting the 3,070,23012/1962 Peterson ..209/310 direction of the -P at different P Spaced3,225,926 12/1965 Dostatni ..209/368 x transversely the direction of the-P The 359,544 3/l887 Russell et ah Wang/357 x stnker assembhes may beoperated synchronously or 878,728 2/1908 Harrop ..209/382 xasynchmnously- Blod ett.....' ..209 347 2131 13322 5%;? Cole ..209 4 03x7 Clam, 8 Draw PATENTED DEC 19 I972 SHEET 2 OF 2 FIG.G

ATTORNEYS,

SCREEN WITH DIFFERENTLY TENSIONED SURFACE ZONES BACKGROUND OF THEINVENTION I The invention relates to a sifting machine of a known typehaving a strainer box, a sieve netting'sheet constructed of a wirenetting or a textile netting having properties similar to a wirenetting, a feed inlet and a discharge opening for the material, andstriker assemblies for the excitation of the sieve netting.

It is known in sifting machines to drive the sieve netting directly bystriking it, the strainer box itself generally remaining at rest; or todrive the netting indirectly by striking the box or frame. In thesifting machine according to the present invention the screen nettingsurface is free and directly struck, and the strainer box remains atrest as the support for all the components and assemblies of the siftingmachine.

It is further known to systematically distribute a number of strikerassemblies over the entire extent of the netting and to have themoperate in synchronism, individually, or in groups. It is also known toclamp the sheet of netting into the strainer box frame either along thelonger sides, along the frontal sides, or along all sides, with rigidedges and with partially substantial pretensioning. A proposal has alsobecome known for clamping the entire sheet of netting withoutpretensioning it, so that it is tensioned only by the weight of thematerial. All these methods of fastening the netting have in common thatthe netting has imparted to it a tension which is uniform over itsentire extent.

In these known sifting machines, the sifting characteristic obtained isdetermined by the tension of the netting and is substantially uniformand unchangeable; its intensity being influenceable only by thevariations in the strikers. This uniform intensity causes the netting tobe stressed differently and it can not be adapted to these variations.Consequently the netting is quickly destroyed. The netting tension cannot follow the varying operating conditions during the passage of thematerial to be screened from the feed-in point to the discharge point,so that the sifting process is also incomplete.

SUMMARY OF THE INVENTION It is an object of the presentinvention toovercome the disadvantages set out above and which promises optimumresults in the sifting process.

This is substantially accomplished according to the present invention bytensioning the netting surface at different points into differenttension levels over its entire extent transverse to the conveyingdirection; which I differing tension levels can be individually appliedand with each tension level having its own associated striker. In thismanner, it is possible to force as many different screeningcharacteristics to the netting over its expanse as there are differenttension levels. Thus, the netting tension may, for example, fall instages from a substantial pretensioning nearest the feed-in point tojust the tension of the material just before the discharge point; whicheven with synchronism of the strikers produces substantially improvedsifting results. If the intensity of the strikers is now changedadditionally from tension level to tension level and, in particular, isadapted to the respective tension level, the strikers possibly operatingin different time patterns from tension level to tension level, thesifting machine can meet all possible conditions imposed on it andrealize an optimum result for the siftingprocess as a result.

A further development of the significant inventive idea of the presentinvention provides for tensioning the netting surface at differentpoints into different tension levels in the direction of conveyance,which different tension levels can also be individually applied. Thismeasure substantially increases the possibilities for variations of thetensioning during the operation of the sifting machine in that, forexample, the netting is provided, in the longitudinal, or conveyingdirection with alternating longitudinal tension levels which may be moreor less strongly tensioned.

A feature of the present invention is that the edges of the sheet ofnetting are in engagement with fastening and tensioning elementscorresponding to the extent and distribution of the tension levels;which elements together, except for the separating spaces betweenadjacent levels, clamp the edges of the netting without interruption.

A further feature of the present invention is that the strikersassociated with the different tension levels have a common drive.

A still further feature of the present invention is that the strikersinclude beater levers which are disposed on a vibrating shaft mounted inthe machine frame and extending transversely below the netting surface.

A particularity for providing a punctiform striker is that protrudingcircular heads, cups or plates having small diameters are disposed onthe vibrating beater levers.

Another feature of the present invention is that th pivot bearings forthe vibrating shaft of the strikers are rubber bearings and thevibrating shaft of the strikers is coupled, via a lever, with anelectromagnetic drive which ismounted, as are the pivot bearings, to theframe of the machine.

A sifting machine constructed according to the present invention permitsthe arbitrary use of a drive subdivided into zones in cooperation with anetting surface which can also be tensioned to different levelscorresponding to the zones; the movable parts being insertable into thestrainer box in a dustfree, airtight, waterfree and maintenance-freemanner while the easy exchangeability of a free sieve netting surface ismaintained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top plan view of a sievenetting surface arranged in the frame of a strainer box.

FIG, 2 is a side elevation, cross-sectional view of the device of FIG.1.

FIG. 3 is a portion of FIG. 2 in reverse orientation.

FIG. 4 is a cross-sectional view taken generally along line A-A of FIG.5 of a detail on an enlarged scale of FIG. 2, showing a fastening andtensioning element.

FIG. 5 is a top plan partial view of the detail of FIG. 4.

FIG. 6 is a side-elevation schematic view of a sifting machine accordingto the present invention which has a plurality of striker assemblies.

FIG. 7 is a detail of a striker assembly taken at right angles withrespect to FIG. 6.

FIG. 8 is a top plan view of the sifting machine of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 through show anembodiment of the present invention without striker assemblies.

FIG. 1 shows a sheet of sieve netting l firmly clamped to a frame 2 of asifting machine by means of a plurality of fastening and tensioningelements such as clamps 3 to define a screening surface. Clamps 3 aredistributed along the edges of the netting l in correspondence with thenumber of tension levels desired. The exact spacing of the clamps 3 is,of course, a matter of choice. In this embodiment, six tension levels,numbered I VI, are provided transverse to the conveying or arrowdirection. Accordingly, six pairs of clamps 3 are oppositely disposedalong both longitudinal edges of the netting 1.

Five clamps 3 are also provided across one end of the netting 1 so thatthe netting l is tensioned into five tension levels in the conveyingdirection. Although these tension levels are not indicated in FIG. 1 inthe manner of zones I-VI, it is apparent that there is one level foreach clamp 3.

FIGS. 2-5 show the details of the clamps 3. In particular, FIGS. 4 and 5clearly show that the clamps 3 include jaws 12 which serve to clamp thenetting 1 to a base plate 12 by means of a bolt and nut 13. In addition,a bolt 14 is provided to adjust the tension of the netting 1 by movingit in a direction perpendicular to the extent of frame member 2. Thisarrangement permits the clamps 3 to be tensionable independently of oneanother so that the desired pretensioning of the netting can beindividually set at different levels. Thus, the tensioning at a givenpoint along the netting can be different from any other point along thenetting.

FIGS. 6-8 show a sifting machine with striker assemblies that may usethe tensioning concept set out above. That is, a netting 1 may again befastened and tensioned by a plurality of clamps 3. The strainer box 6 isprovided with an inlet and an outlet 16, between which the netting 1extends. A plurality of striker assemblies are arranged beneath thesurface of the netting 1.

Each striker assembly is made up of a beater lever 8 which has a head 9and is fastened to a shaft 7 mounted in rubber bearings 5 in the wall ofthe strainer box 6 (FIGS. 6 and 7). Circular head 90f FIGS. 6-8 may havethe form of a cup or plate as well. The shaft 7 is connected to a knownelectromagnetic drive 10 by means of a lever 11. This arrangementpermits the shaft 7 to vibrate in the rubber bearings, utilizing theelasticity of the rubber to vibrate in tune with the drive 10. The drive10 is driven in a known manner at the line frequency, and emitshigh-frequency harmonics when lever 11 contacts it, so that the armaturevibrations of the drive 10 are transmitted to the shaft 7 via lever 11.The rubber bearings 5 additionally provide a dust-free and maintenancefree bearing for the shaft 7.

In the sifting machine according to FIGS. 6 through 8, the strikerassemblies are arranged to occupy defined zones which are associatedwith the respective tension levels, as can be seen from FIG. 8. Thesezones are also identified by the numbering I-VI. A plurality of strikersin one of the zones I-VI may be mounted on a common shaft 7 connected toa single drive 10. This provides a common drive for all of the strikersof a common transverse zone. The striker assemblies associated with thevarious zones can be driven either synchronously or asynchronously bysuitable control means that is well known in the art. For example, eachdrive 10 could be adjusted manually. Therefore, the netting can becontrolled by imposing varying tension levels-as well as by theexcitation of the striker assemblies. Thus, the sifting machineaccording to the present invention can be adapted to any desiredrequirements.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

Iclaim:

1. In a sifting machine including a strainer box with feed-in anddischarge points therein, a one-piece netting defining a material flowsurface and having two opposite end portions, two opposite lateral edgeportions and a free portion extending from one of the edge portions tothe other, means for fastening the two lateral edges to the strainer boxto thereby tension the netting, the netting defining a flow-path for thematerial to be screened said flow-path extending from a feedin point atone end portion of the screen to a discharge point at the other endportion of .the screen and extending longitudinally over the freeportion of the netting, and a plurality of striker assemblies arrangedin the strainer box adjacent to the free portion of the netting fordirect excitation of the netting, the improvement wherein the fasteningmeans comprise a plurality of individual fastening devices which arearranged along the lateral edge portions of the netting and are spacedin the direction of the flow-path for individually tensioning thenetting, in a direction transverse to the flowpath, at different pointsspaced in the direction of the flow-path such that the netting istransversely tensioned to different tensions along said direction of theflowpath, and wherein said striker assemblies are likewise spaced in thedirection of the flow-path for separately exciting the differentlytensioned portions of. the netting.

2. A sifting machine as definedin claim 1, wherein said fastening meanscomprise a plurality of further individual fastening devices which arespaced along one of said end portions for individually tensioning thenetting, in the direction of the flow-path, at different points spacedtransversely to the direction of the flowpath such that the netting islongitudinally tensioned to different tensions along the transversedirection.

3. A sifting machine as defined in claim 1, wherein all of the strikerassemblies .which are aligned in a direction transverse to the flow-pathhave a common drive.

4. A sifting machine as defined in claim 3, wherein each of said strikerassemblies has a beater lever and a vibrating shaft mounted in thestrainer box and operatively coupled with said common drive and saidbeater lever, and wherein said striker assemblies are arranged below thenetting surface.v

lever.

I060ll 0571 sifted flows along a flow-path extending from one end of thenet to the other and between the lateral edges of the net, in adirection transverse to the flow-path such that the netting is tensionedto different tensions at different points spaced in the direction of theflow-path, and applying separate striker excitation to the differentlytensioned portions of the netting.

l III

1. In a sifting machine including a strainer box with feed-in anddischarge points therein, a one-piece netting defining a material flowsurface and having two opposite end portions, two opposite lateral edgeportions and a free portion extending from one of the edge portions tothe other, means for fastening the two lateral edges to the strainer boxto thereby tension the netting, the netting defining a flow-path for thematerial to be screened said flow-path extending from a feed-in point atone end portion of the screen to a discharge point at the other endportion of the screen and extending longitudinally over the free portionof the netting, and a plurality of striker assemblies arranged in thestrainer box adjacent to the free portion of the netting for directexcitation of the netting, the improvement wherein the fastening meanscomprise a plurality of individual fastening devices which are arrangedalong the lateral edge portions of the netting and are spaced in thedirection of the flow-path for individually tensioning the netting, in adirection transverse to the flow-path, at different points spaced in thedirection of the flow-path such that the netting is transverselytensioned to different tensions along said direction of the flowpath,and wherein said striker assemblies are likewise spaced in the directionof the flow-path for separately exciting the differently tensionedportions of the netting.
 2. A sifting machine as defined in claim 1,wherein said fastening means comprise a plurality of further individualfastening devices which are spaced along one of said end portions forindividually tensioning the netting, in the direction of the flow-path,at different points spaced transversely to the direction of theflow-path such that the netting is longitudinally tensioned to differenttensions along the transverse direction.
 3. A sifting machine as definedin claim 1, wherein all of the striker assemblies which are aligned in adirection transverse to the flow-path have a common drive.
 4. A siftingmachine as defined in claim 3, wherein each of said striker assemblieshas a beater lever and a vibrating shaft mounted in the strainer box andoperatively coupled with said common drive and said beater lever, andwherein said striker assemblies are arranged below the netting surface.5. A sifting machine as defined in claim 4, wherein each of said strikerassemblies has a small diameter protruding circular member mounted onsaid beater lever.
 6. A sifting machine as defined in claim 5, furtherincluding rubber bearings for mounting said vibrating shaft, and whereinsaid common drive is an electro-magnetic drive and each of said strikerassemblies has a lever operatively coupled to said electro-magneticdrive and said vibrating shaft.
 7. In a method of sifting material, thesteps of tensioning a one-piece netting, over which material to besifted flows along a flow-path extending from one end of the net to theother and between the lateral edges of the net, in a directiontransverse to the flow-path such that the netting is tensioned todifferent tensions at different points spaced in the direction of theflow-path, and applying separate striker excitation to the differentlytensioned portions of the netting.